#include<stdio.h>
#include"math.h"
    
     int main()
    {
        double e=0.1,b=0.5,c,d;
        long int i;
        for (i=6; ;i*=2)
        {
            d=1.0-sqrt(1.0-b*b);
            b=0.5*sqrt(b*b+d*d);
            if (2*i*b-i*e<1e-15) break;
            e=b;
        }
        printf (" pai=%.15lf\n",2*i*b);
        printf (" The number of edges of required polygon:%ld\n",i);
    }
